A common problem with driving a transport truck during the winter is that the turbulence created by the moving transport swirls up flurries of snow which pack against the rear end of the trailer, covering the braking and turning lights of the vehicle. The operator of the transport must stop frequently, especially at night, to clean the light lenses to prevent accident from a following driver.
One difficulty in providing light wiping function on a transport trailer is that a source of power for operating such device is often a restricted one. The number of electrical conductors in the service cable from the truck to the trailer is, in many cases, limited to power supply to the position lights, signal lights, brake lights, and a third axle lifting mechanism. Similarly, the air power supply to-the trailer brake actuators is conforming to strict safety regulations, and a taping into an air line must not alter the performance of the braking system.
Another obstacle in providing light wiping functions on a transport trailer is that the wiping device must be adaptable to existing trailers with as few modifications as possible. Furthermore, if the installation is done by a person having limited knowledge of electricity and pneumatic, the installation instructions must be easily understood such that an installer will not tamper with the safety aspects of the vehicle.
A number of prior art devices have been developed for cleaning light lenses, and especially for cleaning the head lights of a vehicle having a compressed air system. For example U.S. Pat. No. 4,505,001 issued Mar. 19, 1985 to Fasolino describes a high pressure nozzle in combination with a flexible tube whipping from side to side against the surface of the light. The high pressure nozzle discharges cleaning fluid against the surface of the lens, while the whipping effect of the tube is obtained by forcing a stream of air under high pressure through the tube.
Another example of an air wiping system is described in U.S. Pat. No. 5,083,339 issued Jan. 28, 1992 to Bristow. The device uses a wiper arm driven by a pneumatic motor. The arm has a plurality of apertures through which a mixture of air and cleaning fluid is ejected under high pressure against the surface of a headlight.
In both the previously described inventions, the operation of the wiper is continuous upon energizing the system by the driver. The flow of air from the vehicle's air reservoir is also continuous during the operation of the wipers. Such a constant outflow of air from a truck's air brake system is not desirable because it may affect the performance of the air brake system of the vehicle, as will next be explained.
According to an aforesaid comment, an air brake supply system of a vehicle is made to comply to safety standards from regulatory bodies. For example, an air brake supply system for a transport truck must comprise an air reservoir on the truck which has the volume of at least 12 times the combined volume of all service brake chambers at a maximum displacement of the pistons or diaphragms. Similarly, the trailer must be equipped with one or more air reservoirs having a combined volume of air that is at least 8 times the combined volumes of all service brake chambers. The air pressure in those reservoirs must be maintained preferably at above 100 psi, and not less than 90 psi. The compressor of the truck must be capable of building air pressure within the system after every use of the brakes. Typically, the requirement is that the compressor must be capable of building up air pressure in the air system from 85 psi to 100 psi within 25 seconds.
Thus, an air wiping device which continually drains air from the air brake system may require a larger compressor on the vehicle to ensure compliance to the required performance of the safety standard. Moreover, such a continuous outflow of air of the prior art devices may cause the compressor to engage often to make up the system pressure, and may increase thereby the fuel consumption of the vehicle.
Other air wiping systems to remove snow from vehicle mirrors and windows are described in U.S. Pat. No. 5,097,563 issued on Mar. 24, 1992 to Cowan, and in U.S. Pat. No. 5,140,719 issued on Aug. 25, 1992, also to Cowan. These systems comprise a blower to deliver a pre-heated high velocity air stream to nozzles located adjacent the surfaces to be cleaned.
An installation of such a blower and a heater under a transport trailer would likely require intricate housing to protect the devices and nozzles from the climate and road splashes. Such installation would also probably require the upgrading of the service cable from the truck to the trailer to supply electrical energy to the blower and the heater.
Another prior art device for cleaning the lenses of vehicle's lights is disclosed in Canadian Patent no. 1,131,858 issued on Sept. 21, 1982 to Savage et al. The system comprises a source of compressed air, pressure accumulators, regulator valve, check valve, directional valve, a reservoir of washing fluid and delivery nozzles.
Likewise, the complexity of the proposed piping of this invention renders it difficult for retrofitting the equipment on a transport trailer by a person unexperienced with pneumatics.
Furthermore, another inconvenience with an air wiping system installed near the rear lights of a transport trailer is that when the system is not in use, the orifice of a prior art nozzle may freeze from snow and slush accumulating thereon, rendering thereby the system inoperative.